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  #1  
Old 02-14-2012
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Heart Cardiac Muscle Contraction

Select the false statement regarding the cardiac muscle contraction?

A) Initiation of cardiac muscle contraction is through fast opening of voltage-gated sodium channels.
B) The slight repolarization after the initial large increase in membrane potential is due to closure of voltage-gated sodium channels and transient potassium efflux through ungated potassium channels.
C) Slow calcium channels are responsible for the development of plateau phase in cardiac muscle contraction.
D) The fast repolarization after plateau phase of cardiac muscle contraction is mainly due to opening of delayed rectifier potassium channels.
E) The delayed rectifying potassium channels are responsible for the relative refractory period during early phase 4.
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C is false
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B) The slight repolarization after the initial large increase in membrane potential is due to closure of voltage-gated sodium channels and transient potassium efflux through ungated potassium channels.
(this part is incorrect)

it is due to closure of sodium
n opening of potassium channels... (the fast ones)
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E?

isnt it the Na+/K+-ATPase that mainly regulates phase 4?
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Old 02-14-2012
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Ans is.......... A............. in cardiac muscle contraction its due to funny Na channel which are slow not fast voltage gated Na which is seen in skeletal muscle .............
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i feel its B........THE SLIGHT REPOLARISTION after the initial spike is due to closure of sodium channels and opening of calcium channels........
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Quote:
Originally Posted by Hitman View Post
Ans is.......... A............. in cardiac muscle contraction its due to funny Na channel which are slow not fast voltage gated Na which is seen in skeletal muscle .............
You are right but that's in conduction tissue not muscle. In muscle it is fast voltage gated Na channels.
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Quote:
Originally Posted by val7 View Post
C is false
The plateau or phase 2 occurs because of the voltage gated Ca channels.
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Old 02-14-2012
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Quote:
Originally Posted by mbbs2010 View Post
B) The slight repolarization after the initial large increase in membrane potential is due to closure of voltage-gated sodium channels and transient potassium efflux through ungated potassium channels.
(this part is incorrect)

it is due to closure of sodium
n opening of potassium channels... (the fast ones)
this is the right answer.

It is the voltage gated K channels that open not the ungated ones.
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I would say B...
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Old 02-15-2012
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Quote:
Originally Posted by mbbs2010 View Post
B) The slight repolarization after the initial large increase in membrane potential is due to closure of voltage-gated sodium channels and transient potassium efflux through ungated potassium channels.
(this part is incorrect)

it is due to closure of sodium
n opening of potassium channels... (the fast ones)
perfect explanation
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Old 03-31-2012
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C is answer
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Old 03-31-2012
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the incorrect statement is B.

The phase 1 (overshoot) is due to closure of voltage-gated fast Na channels and the opening of iKto channels (transient outward K+ current). Depolarization produced by Na+ influx leads to activation of a transient outward current mainly carried by K+. This current is called ITO. As the activation of ITO is transient, only a brief efflux of K+ occurs, causing a brief and limited repolarization.
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Old 03-31-2012
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Quote:
Originally Posted by Dr.NickRiviera View Post
E?

isnt it the Na+/K+-ATPase that mainly regulates phase 4?
Yeah... I also think so... and is mainly Na the one controlling phase 4... right???
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I'd say C is the right answer. Here goes my explanation-
phase 1 is due to closure of voltage gated Na channels and transient efflux of K via UNGATED channels, as depolarisation by then wd have already closed the VOLTAGE gated iK1(inward rectifying current) channels.
phase 2 developement is mainly dependent on the closure of these iK1 channels and also slow influx of Ca.
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Old 03-31-2012
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Quote:
Originally Posted by Dr. Mexito View Post
Yeah... I also think so... and is mainly Na the one controlling phase 4... right???
Now that I'm thinking about it... C is about SA and Av nodes, and the rest is about ventricles???

If so, then I think C is the correct answer....
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Old 01-27-2013
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Default d

d is the right answer
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